1. Field of the Invention
The invention relates to force transmission through a mechanical linkage, especially a cable system which provides remote actuation of brake or clutch devices used on lightweight vehicles.
2. Description of Prior Art
Many lightweight vehicles such as motorcycles, bicycles, wheelchairs, aircraft, lawn mowers, etc. incorporate manually actuated mechanical linkages for clutches, brakes, gear changers and other devices. Manual actuation is usually achieved by hand grip control lever means or foot lever meanss. The actuation force available through manual effort is limited to the capacity of human strength. An average adult male can exert approximately 45 pounds of force on a one hand grip lever means with a throw (actuation distance) of about four inches.
The actuating mechanism; hand lever means, foot pedal, etc. is designed to enable the user to exert enough force to overcome a return spring, cable and pulley friction and the resistance of the actuated device. The total force required is often greater than human capacity so that mechanical advantage is usually designed into the actuating mechanism and/or the actuated device. The cable linkage actuating control lever means is a good example of a prior art application of mechanical advantage. U.S. Pat. No. 4,149,432, titled "Cycle Handlebar Lever For Brake Or Clutch Control", issued Apr. 17, 1979 to inventor Mark A. Costahaude, teaches a means for achieving mechanical advantage in order to reduce the manual force required to actuate a linkage system. U.S. Pat. No. 4,301,694, titled "Hand Operated Lever Linkage Control", issued Nov. 24, 1981 to inventor Larry J. Costa, shows a method for mechanical advantage with adjustable means mounted on a control lever.
Cables are most often used in conjunction with mechanical linkages to transmit actuation forces over short distances. Actuation cables of this type usually side within a tight fitting, flexible, steel sleeve which need only be anchored at its end points. Other cable systems use free cables routed over pulleys in order to change direction, achieve mechanical advantage, etc. Other linkage systems use link bars or chains of various construction to achieve greater strength and flexibility.
During the useful life of a mechanical linkage assembly, lubricants dry out, mechanical parts wear and the metal work hardening occurs in springs. The manual effort required for actuation tends to increase with the age of the linkage system. The operation of standard linkage systems by the very young, the very old, the infirm or others whose capabilities lie outside the range of strength for which a system is designed, presents a problem for which no simple prior art solution exists. No prior art device has been found which may be easily installed into existing linkage assemblies, without modifying them, which will reduce the manual force required for actuation. No prior art device has been found which is specifically designed to be retrofitted into an existing cable actuation system.